The 100th Volume Memorial Special Issue of Tetsu-to-Hagané “Progress in Steel Science and Technology toward a Future of Sustainable Innovation Part 4: Subject and Deployment of Analytical Technology in Steelmaking Process”

Chemical methods of analysis of steel samples are significantly considered in the perspective of precision, trueness and accuracy of analytical results, as the standardization for control of iron and steel making process. On the other hand, automatic apparatus for wet chemical analysis have been required, in relation to rationalize the analytical procedures with complicated pre-treatment steps taking a lot of skill and time. In the present paper, Automatic Photometric Analyzers, Technicon AutoAnalyzers and Flow Injection Analysis (FIA) systems for the automation of wet chemical analysis, which have been developed during the last several decades, were reviewed. Especially, FIA systems has been examined studiously due to low reagent and sample consumption, good reproducibility and repeatability, minimal sample contamination in a closed analytical system, and reduced skill and time for analysis. Applications of FIA for Bi, Mn, N, B, Mo, and Cr in steel samples, and electrolytic decomposition method of steel samples were mentioned particularly. The prospective developments of automatic techniques of chemical analysis in future were also proposed.

Analytical methods based on atomic emission spectroscopy are capable of simultaneously measuring multiple elements. They can be powerful tools in process control especially when sample preparation is simple and not time-consuming. In the present paper, elemental analytical techniques utilizing the lasers and a glow discharge emission spectrometry (GDOES) are reviewed with regards to their applications for steelmaking process control. They are different from the conventional spark discharge optical emission spectrometry (SDOES) in the atomization, the generation of plasmas and their characteristics. Accordingly, these techniques have been developed to make use of their properties in the applications for steelmaking processes. GDOES is characterized by its ability in rapid depth profiling and has been utilized in analyzing surfaces of materials including galvanized steels. Laser-induced breakdown spectrometry (LIBS), one of the main laser spectroscopic techniques, has been applied for rapid evaluation of steel defects taking advantage of laser’s pointability. LIBS is also distinguishable from other methods in its capabilities in stand-off and contactless analyses. The prospect of a direct analysis of molten steel, using lasers in particular, is also mentioned.

This article attempts to give an overview of analytical atomic spectrometry in combination with inductively coupled plasma (ICP) and microwave induced plasma (MIP) for the determination of trace elements in iron and steel. The aim is to introduce, in a first part, recent trends in ICP-atomic emission spectrometry (AES) and ICP-mass spectrometry (MS) in terms of sample dissolution, interference study, chemical separation of the analyte elements, sample introduction technique and isotope dilution method utilized only for ICP-MS. In a second part, this paper is meant for a basic information for a description of high-power MIP produced using an Okamoto cavity for AES, especially its combination with hydride introduction into an MIP. High-power nitrogen MIP-AES has successfully coupled with hydride introduction technique for the single- and multi-element determination of several hydride-forming elements in iron and steel samples. Finally, conclusive remarks will be depicted for ICP-AES, ICP-MS and MIP-AES in the steel-making industry.

Metallic materials as represented by steels mostly contain various precipitates such as nitrides, carbides and inter-metallic compounds in addition to non-metallic inclusions, oxides and sulfides. These are present as an inevitable former or by design. Those varieties, size and distribution types are very wide then one of important structural factors that affects on various properties of materials.Therefore, accurate analysis of them is considerable significance to control target properties of materials reproducibly. In the steel research field, study of analytical methods for inclusion in steels has been actively conducting since 1960’s. Especially in chemical analysis method, systematization and standardization like JIS has been promoted by corroborated researches in an ISIJ. Previously established methods and detail of analysis of chemical states have been described in publications edited by ISIJ and comprehensive review paper has been issued by Takayama. In this short article, direct observation methods with microscopy, rapid analysis categorized as instrumental analyses, non-destructive inspections and extraction method for non-metallic inclusions are briefly reviewed.

Activation analysis has developed as one of trace element analysis. Atom of analyte is activated with nuclear reactions by neutron from nuclear reactor, charged particle from an accelerator or photon from an accelerator. Radiations from activated nuclides are measured with a gamma spectrometer, and determined with compare of the standard. These methods are called as neutron activation analysis (NAA), charged particle activation analysis (CPAA) or photon activation analysis (PAA), respectively. And prompt gamma-ray analysis (PGA) and neutron depth profiling (NDP) measuring prompt gamma-rays and prompt charged particles, respectively, from nuclear reactions with low energy neutrons are able to be used. In the field of iron and steel, the numbers of applications for activation analysis are a few except NAA. This paper reviews applications of NAA and CPAA for various iron and steel and reviews principles and characteristics, analysis systems and analytical methods, as well as applications of PGA and NDP.

Various investigations were conducted to establish quantification of microelements in iron and steel using ICP–MS with solid-phase extractive separation capable of separating the matrix simply and rapidly as a pretreatment. A “zero-emission type analysis” free from EDTA as a masking agent and buffering agents used for pH adjustment was sought. To do so, an anion-exchange type solid-phase extraction disk was used as the solid-phase extraction agent, along with “skill-free analysis” requiring no cumbersome manipulations, and “quick analysis” for assessment in an extremely short period of time. Results show a target element in a solid-phase disk, whereas the sample solution at separation was maintained at higher than pH 1.8. The pH adjustment was conducted by dilution of the sample solution with about 400 cm3 of water. The target element held in the solid-phase disk was eluted with 10 cm3 of 3 kmol/m3 nitric acid. The detection limitations [3 σ; ng/g (ppb)] were the following: Ti 0.043, Ge 0.014, Zr 0.013, Nb 0.025, Mo 1.06, Sn 0.030, Hf 0.010, Ta 0.019, and W 0.12.

The majority of engineering steels are ferromagnetic and structually inhomogeneous on special scales ranging from nanometers to micrometers, and physical properties of engineering steels arise from three-dimensional (3D) features of the microstructure. Thus, obtaining 3D representation with a large field of view is desired for transmission electron microscopy (TEM) based microstructure characterization to establish microstructure - physical properties relationships with reasonable statistical relevancy. Here, we venture to use a conventional sample preparation process,i.e., mechanical polishing followed by electro-polishing, and experimental protocols optimization for electron tomography (ET) for ferromagnetic materials, especially engineering steels’ microstructural characterization are carried out. We found that the sample thickness after the mechanical polishing step is a critical experimental parameter affecting the success rate of tilt-series image acquisition. For example, for a ferritic heat-resistant 9Cr steel with lath martensite structure, mechanically thinning down to 30 μm or thinner was necessary to acquire an adequate tilt-series image of carbide precipitates in the high-angle annular dark-field scanning TEM (HAADF-STEM) mode. On the other hand, tilt-series image acquisition from dislocation structures remains challenging because the electron beam deflection during specimen-tilt was unavoidable and significant in the HAADF-STEM mode. To overcome the electron beam deflection problem, we evaluate several relatively accessible approaches including the “Low-Mag and Lorentz” TEM/STEM modes; although they are rarely used for ET, both the modes reduce or even zero the objective lens current and likely weaken the magnetic interference between the ferromagnetic specimen and the objective lens magnetic field. The advantages and disadvantages of those experimental components are discussed.

Details of corrosion process under the coating layer of the steel sheet have not been understood well. Therefore, it is required to develop a nondestructive analytical method for the near surface of the steel sheet. It is also required to have analytical tool for observing the corrosion process in the solution. The authors developed a confocal 3D-XRF analytical instrument, which enables a nondestructive elemental analysis near the surface of the material. This technique was applied for analyzing the corrosion process under the coating layer of the steel sheet. Depth elemental images showing elemental distributions were nondestructively obtained. 3D-XRF method was also applied for observing Fe distribution in the NaCl solution during corrosion of Fe from the steel sheet. Dissolution, migration, and deposition processes were successfully monitored. It is expected that this confocal 3D-XRF technique will be applied for in-situ analysis of the steels under various environments.

We have recently realized an electron probe microanalyzer (EPMA) and cathodoluminescence (CL) spectrometer with a palm-top size chamber including the electron source and the sample stage using a pyroelectric crystal as the electron source. In the present study, we carried out microanalysis and elemental mapping using the portable EPMA and CL spectrometer. As for the portable EPMA, the electron beam bombarded a sample and the wall of the stainless steel chamber due to using a LiTaO3 single crystal with a cuboidal shape. The electron beam was focused on the sample by setting a metal needle on the pyroelectric crystal and covering the needle holder with an insulating material. The spot size of the focused electron beam was 300 μm. We succeeded in elemental analysis in micro-scale region using the focused electron beam. The portable EPMA can also detect light elements such as Mg, Al and Si by introducing the X-ray detector into sample chamber. The portable CL spectrometer can detect ppm order of rare-earth elements in a mineral ore. The portable CL spectrometer can also perform an elemental mapping of rare-earth elements by capturing a CL image with CMOS camera.

Changes in solution properties of ethyleneglycol during dissolving calcium oxide were investigated in terms of reinvestigation of the ethyleneglycol method to determine free calcium oxide in steel slags precisely. Dissolution of calcium oxide into ethyleneglycol produced water as a result of chemical reaction between the both entities. As increase in the amounts of calcium oxide dissolved into ethyleneglycol, viscosity of the solution increased with being cloud. Dissolution of calcium oxide from 0.1 g to 0.6 g into 20 mL of ethyleneglycol made the solution a turbid gel. TOF-MS and LC-MS analyses confirmed that oligomerization of ethyleneglycol in the ethyleneglycol solution proceeded to produce many kinds of oligomers of ethyleneglycol. Addition of a partially-halogenated alcohol into the ethyleneglycol solution suppressed change in properties of the solvent, such as increase of viscosity, color development and gelation. Especially, addition of 2,2,2 -trifluoroethanol reduced the variation of analytical values of free calcium oxide contents in the steel slag even though slight decrease in the analytical values.

Silica is a nutrient for diatom, which is a phytoplankton in oceans. We thus study the possibility of generating silica from steelmaking slag. Silicic acid present in steelmaking slag comprising of sodium chloride was examined. When non-carbonated slag and carbonated slag sample in solutions consisting of 0.5 mol dm–3 sodium chloride were shaken for a week, a slightly higher pH for carbonated slag solution was observed. The concentration of extracted silicic acid from carbonated slag was higher than that from non-carbonated slag. Both solutions contained high concentrations of calcium ions.Silicic acids show several chemical forms in solutions. The silicic acids contained in both non-carbonated and carbonated slag solutions were identified with FAB-MS (fast atom bombardment mass spectrometry): [Si(OH)2O2Na]–, [Si(OH)O3Ca]–, [Si2(OH)5O2]– ([dimer]–), [Si2(OH)4O3Na]–, [Si4(OH)7O5]– ([cyclic tetramer]–), [Si4(OH)6O6Na]–, [Si4(OH)9O4]– ([linear tetramer]–), and [Si4(OH)8O5Na]–. Among all these complexes the diatom uptakes [dimer]–, and [linear tetramer]–. The silicic acids in both solutions also showed almost the same peak intensity ratios of [Si(OH)2O2Na]–, [Si(OH)O3Ca]–, [dimer]–, and [linear tetramer]– against [cyclic tetramer]. As a result, we consider carbonated slag to be a better supplier of silica to seawater than non-carbonated slag.